A metal-air battery is a battery wherein air (oxygen) is used as a cathode active material. The metal-air battery has advantages such as: the energy density is high; and the battery can be easily made small and light. At present, therefore, such battery attracts attention as high-capacity battery which excels widely used lithium ion batteries.
Such a metal-air battery comprises, for example, an air cathode layer having a conductive material (such as carbon black), a catalyst (such as manganese dioxide) and a binder (such as polyvinylidene fluoride), an air cathode current collector for collecting current of the air cathode layer, an anode layer containing an anode active material (such as metallic Li), an anode current collector for collecting current of the anode layer, and an electrolyte (such as nonaqueous electrolyte solution).
Conventionally, metal-air batteries using various catalysts have been known. For example, Non-Patent Document 1 discloses a nonaqueous electrolyte solution type lithium air battery wherein EMD (electrolyte manganese dioxide, γ-MnO2) is used as a catalyst. Furthermore, the document discloses that this battery can give an initial discharge capacity of 1000 mAh/g-C, 50 charge-discharge cycles can be attained, and the capacity retention (R10/1) after 10 cycles, with respect to the initial discharge capacity, is about 80%. Moreover, Non-Patent Document 2 discloses a nonaqueous electrolyte solution type lithium air battery wherein α-MnO2 in nano-wire form is used as a catalyst. Furthermore, the document discloses that this battery gives an initial discharge capacity of 3000 mAh/g-C. However, in the battery using α-MnO2 in nano-wire form, a large deterioration in capacity is caused while the battery is repeatedly charged and discharged. Thus, the capacity retention (R10/1) after 10 cycles, with respect to the initial discharge capacity, is as low as about 50%.